In-depth | hyDroDynamiCS
Meeting the hydrodynamicist’s needs
Successful hydrodynamic analysis depends on using the proper tool for the
problem to be solved. Making design tools work for you is only possible, say
HydroComp, Inc if you understand the limitations of the available tools.
H
ydrodynamics is a very broad
discipline that includes speed
and power prediction, hull
form analysis, propulsor design, and
other tasks. The tools that we employ
to solve hydrodynamic problems range
from simple plots and spreadsheets to
very complex computational codes and
model testing.
Empirical or Computational
It is useful to distinguish between Table 1 Summary of hydrodynamic analysis solutions.
‘quantitative’ problems encountered
in naval architectural design, such as
the prediction of hull drag or propeller
thrust, and those problems that are
‘qualitative’, visualisation of flow,
comparisons between design variants
for example. Identifying the nature of
the problem is key to the successful
application of the proper solution.
The ‘gold standard’ of hydrodynamic
analysis is model testing, but this can
be costly to employ as an integral part Table 2 Scope of data definition for different solutions.
of the design cycle for most projects.
For questions of a quantitative bent,
empirically based analysis solutions use of empirically based analyses can very powerful and capable – so long
(such as statistical methods, systematic effectively provide qualitative results, as the problem is well defined and of a
series and sea trial evaluation) are but not to the same localised degree as a qualitative nature.
still the real workhorses of day-to-day computational code. To illustrate just what is needed for a
hydrodynamic analysis. Most designers reliable application of CFD HydroComp,
simply want to reliably predict vessel drag What about CFD? Inc. was recently contracted to
or determine propeller performance, for There has been an upswing in the broad participate in an investigation of a noise
example, than to tweak the hull form or commercial interest in computational and vibration problem on a sizeable
visualise a flow problem. fluid dynamics (CFD). For problems passenger vessel. In our development
Where empirical solutions of visualisation and local details, CFD of knowledge about the inflow to
directly serve quantitative problems, has become a viable option. For many the propeller, we collaborated with
computational solutions are most problems, it is the ideal solution, but it a colleague that has over 20 years of
suitable for qualitative problems of is not without its caveats and must be hydrodynamic experience, including
visualisation and comparison. The employed carefully. extensive familiarity with CFD. We
numerical nature of a computational A reliable application of CFD still achieved the expected results, but
solution is self-regulating (to a point), requires deep pockets and specialised even with his specialised expertise, the
so that small changes in geometry training. One issue of concern is modelling was difficult and calculations
can effect a corresponding change in simply a problem of expectation. Many were repeated. Only through his
analysis results. proponents of CFD propose that it is the knowledge of the codes was he able
Model tests can also provide qualitative solution for all things hydrodynamic, to deduce that the initial results were
solutions, but generally at much higher which results in unrealistic expectations inaccurate and required a different
cost and effort, likewise the careful for the use of the tool. CFD is indeed modelling scheme.
32 The Naval Architect January 2010
NA Jan 10 - p32+33+34.indd 32 12/01/2010 09:56:04
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